Taking visitors to the tranquil depths of Istanbul, the Basilica Cistern is the city’s largest covered reservoir. Built in 532 AD on the site of a great basilica, the Basilica Cistern once supplied water to nearby palaces such as the Great Palace of Constantinople and Topkapi Palace.

Also known as the Sunken Palace, the underground site takes up 9,800m2 and has the capacity to store up to 100, 000 tons of water. The water which fed the Cistern came through a viaduct, which connected the source of supply at Belgrade Forest to the Basilica Cistern, a distance of about 19km. Five meter thick walls surround the Cistern and are specially coated to ensure waterproofing.

Its domed ceilings are held up by intricately designed marble and granite columns which vary in style between Corinthian, Doric and Ionic. There are 336 columns in all, arranged in 12 rows of 28 columns.

There are two columns of particular interest at the Basilica Cistern; those bearing the head of Medusa. Medusa is a female monster from Greek mythology with hair made of snakes, which is said to have turned those who looked at her into stone. She was beheaded by the hero Perseus who then gave her head to Athena to use as a weapon on the top of her shield as a way of averting evil.

Medusa’s upside down head is found on the base of one column. There are various theories surrounding why her head was placed upside down, but many believe that it was done to ward off evil spirits.

Next to the upside down head is another head depicting Medusa which has been placed sideways. Why the two heads were placed in different directions has only served to deepen the mystery, but some think that placing the heads in the same direction would give rise to evil forces.

Massive restoration was required to make the Basilica Cistern as visitor-friendly as it is today. In 1985, 50,000 tons of mud was removed from the site and walking platforms were constructed; in 1994, another revamp was carried out.

Now, visitors can stroll along the platforms and watch resident goldfish swim in the Cistern’s cool waters. The Basilica Cistern also houses its own candlelit café, where soft lighting and classical music contributes to the overall atmosphere of the place.

Nowadays, Basilica Cistern has gained another fame in people who like to read the novels of Dan Brown. At his last book named with “Inferno”, Bailica Cistern is one of the fantastic places which usually hide clues of a secret.